Investigation of thermal expansion and compressibility of rare-earth orthovanadates using a dielectric chemical bond method

The chemical bond properties, lattice energies, linear expansion coefficients, and mechanical properties of ReVO4 (Re = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Sc, Y) are investigated systematically by the dielectric chemical bond theory. The calculated results show that the covalencies of Re-O bonds are increasing slightly from La to Lu and that the covalencies of V-O bonds in crystals are decreasing slightly from La to Lu. The linear expansion coefficients decrease progressively from LaVO4 to LuVO4; on the contrary, the bulk moduli increase progressively. Our calculated results are in good agreement with some experimental values for linear expansion coefficients and bulk moduli.

Hydrothermal Synthesis, Structures, and Luminescent Properties of Seven d(10) Metal-Organic Frameworks Based on 9,9-Dipropylfluorene-2,7-Dicarboxylic Acid (H(2)DFDA)

A series of Zn(II) and Cd(II) metal-organic frameworks, namely, [Zn(DFDA)] (1), [Cd(DFDA)(C2H5OH)] (2), [Zn-2(DFDA)(2)(L-1)(2)](2) center dot 3H(2)O (3), [Cd-2(DFDA)(2)(L-1)(2)] (4), [Zn(DFDA)(L-2)] (5), [Cd(DFDA)(L-2)(DMF)] (6), and [Zn(DFDA)(L-3)] (7) (where DFDA = 9,9-dipropylfluorene-2,7-dicarboxylate anion, L-1 = 1,4-bis(imidazol-1-ylmethyl)benzene, L-2 = 1,1'-(1,4-butanediyl) bis(imidazole), L-3 = 2,2'-bipyridine) have been synthesized under hydrothermal conditions and structurally characterized. Compound 1 exhibits a three-dimensional (3D framework containing one-dimensional (1D) Zn(II)-O clusters, with (4(8).6(7)) topology. Compound 2 contains hydrophobic channels built from infinite 1D Cd(II)-O clusters, with (4(8).5(4).6(3)) topology.

Metal-organic frameworks based on the pyridine-2,3-dicarboxylate and a flexible bispyridyl ligand: syntheses, structures, and photoluminescence

Three new metal-organic coordination polymers, [Cu(2,3-pydc)(bpp)]center dot 2.5H(2)O (1), [Zn(2,3-pydc)(bpp)]center dot 2.5H(2)O (2) and [Cd(2,3-pydc)(bpp)(H2O)]center dot 3H(2)O (3) (2,3-pydcH(2) = pyridine-2,3-dicarboxylic acid, bpp 1,3-bis(4-pyridyl)propane), have been synthesized at room temvperature. All complexes have metal ions serving as 4-connected nodes but represent two quite different structural motifs. Complexes 1 and 2 are isomorphous, both of which feature 2D -> 3D parallel interpenetration. Each two-dimensional (2D) layer with (4, 4) topology is interlocked by two nearest neighbours, one above and one below, thus leading to an unusual 3D motif. Complex 3 has a non-interpenetrating 3D CdSO4 framework with cavities occupied by uncoordinated water molecules.

Synthesis and Characterization of One-Dimensional and Molecular M(tren)InAsS4 (M = Mn, Co, and Zn) Compounds with a Noncondensed AsS33- Unit

Four transition-metal-amine complexes incorporating indium thioarsenates with the general formula M(tren)InAsS4 (M=Mn, Co, and Zn) and a noncondensed AsS33- unit have been prepared and characterized. Single-crystal X-ray diffraction analyses show that compound 1 (M=Mn) crystallizes in the triclinic crystal system (space group: P (1) over bar) and consists of a one-dimensional (1D) inorganic (1)(infinity){[InAsS4](2-)} chain and [Mn(tren)](2+) groups bonded to the opposite sides of an eight-membered In2As2S4 ring along the backbone of the infinite inorganic chains. Compounds 2 (M=Mn), 3 (M=Zn), and 4 (M=Co) are isomorphous molecular compounds. They all crystallize in the monoclinic crystal system (space group: P2(1)/c). The Mn2+ cation of [Mn(tren)](2+) in 1 has a distorted octahedral environment, while the transition-metal cations of [M(tren)](2+) in the other three compounds locate in trigonal-bipyramidal environments.

Preparation and Luminescence Properties of Gd2MoO6:Eu3+ Nanofibers and Nanobelts by Electrospinning

Gd2MoO6:Eu3+ nanofibers and nanobelts have been prepared by a combination method of the sol-gel process and electrospinning. X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy, photoluminescence, and low voltage cathodoluminescence as well as kinetic decays were used to characterize the resulting samples. The results of XRD and FTIR indicate that the Gd2MoO6:Eu3+ samples have crystallized at 600 degrees C with the monoclinic (alpha) structure. The SEM and TEM results indicate that the as-formed precursor fibers and belts are uniform and that the as-prepared nanofibers and nanobelts consist of nanoparticles. Gd2MoO6:Eu3+ phosphors show their strong characteristic emission under UV excitation (353 nm) and low voltage electron-beam excitation (3 kV), making the materials have potential applications in fluorescent lamps and field-emission displays.

Luminescent Boron-Contained Ladder-Type pi-Conjugated Compounds

Four diboron-contained ladder-type pi-conjugated compounds 1-4 were designed and synthesized. Their thermal, photophysical, electrochemical properties, as well as density functional theory calculations, were fully investigated. The single crystals of compounds 1 and 3 were grown, and their crystal structures were determined by X-ray diffraction analysis. Both compounds have a ladder-type g-conjugated framework. Compounds I and 2 possess high thermal stabilities, moderate solid-state fluorescence quantum yields, as well as stable redox properties, indicating that they are possible candidates for emitters and charge-transporting materials in electroluminescent (EL) devices. The double-layer device with the configuration of [ITO/NPB (40 nm)/1 or 2 (70 nm)/LiF (0.5 nm)/Al (200 nm)] exhibited good EL performance with the maximum brightness exceeding 8000 cd/m(2).

Four New Lanthanide-Nitronyl Nitroxide (Ln(III)=Pr-III, Sm-III, Eu-III, Tm-III) Complexes and a Tb-III Complex Exhibiting Single-Molecule Magnet Behavior

Five new complexes based on rare-earth-radical [Ln(hfac)(3)(NIT-5-Br-3py)](2) (Ln=Pr (1), Sm (2), Eu (3), Tb (4), Tm (5); hfac = hexafluoroacetylacetonate; NIT-5-Br-3py = 2-(4,4,5,5-tetramethyl-3-oxylimidazoline-1-oxide)-5-bromo-3-pyridine) have been synthesized and characterized by X-ray crystal diffraction. The single-crystal structures show that these complexes have similar structures, in which a NIT-5-Br-3py molecule acts as a bridging ligand linking two Ln(III) ions through the oxygen atom of the N-O group and nitrogen atom from the pyridine ring to form a four-spin system. Both static and dynamic magnetic properties were measured for complex 4, which exhibits single-molecule magnetism behavior.

Two-Step Spin-Transition Iron(III) Compound with a Wide [High Spin-Low Spin] Plateau

A new iron(III) coordination compound exhibiting a two-step spin-transition behavior with a remarkably wide [HS-LS] plateau of about 45 K has been synthesized from a hydrazino Schiff-base ligand with an N,N,O donor set, namely 2-methoxy-6-(pyridine-2-ylhydrazonomethyl) phenol (Hmph). The single-crystal X-ray structure of the coordination compound {[Fe(mph)(2)](ClO4)(MeOH)(0.5)(H2O)(0.5)}(2) (1) determined at 150 K reveals the presence of two slightly different iron(III) centers in pseudo-octahedral environments generated by two deprotonated tridentate mph ligands. The presence of hydrogen bonding interactions, instigated by the well-designed ligand, may justify the occurrence of the abrupt transitions. 1 has been characterized by temperature-dependent magnetic susceptibility measurements, EPR spectroscopy, differential scanning calorimetry, and Fe-51 Mossbauer spectroscopy, which all confirm the occurrence of a two-step transition. In addition, the iron(III) species in the high-spin state has been trapped and characterized by rapid cooling EPR studies.

Thermal stability, crystallization, structure and morphology of syndiotactic 1,2-polybutadiene/organoclay nanocomposite

Syndiotactic 1,2-polybutadiene/organoclay nanocomposites were prepared and characterized by thermogravimetry analysis (TGA), X-ray diffraction (XRD), polarized optical microscopy (POM), and differential scanning calorimetry (DSC), respectively. The XRD shows that exfoliated nanocomposites are formed dominantly at lower clay concentrations (less than 2%), at higher clay contents intercalated nanocomposites dominate. At the same time, the XRD indicates that the crystal structures of sPB formed in the sPB/organoclay nanocomposites do not vary, only the relative intensity of the peaks corresponding to (0 1 0) and (2 0 0)/(1 1 0) crystal planes, respectively, varies. The DSC and POM indicate that organoclay layers can improve cooling crystallization temperature, crystallization rate and reducing the spherulite sizes of sPB. TGA shows that under argon flow the nanocomposites exhibit slight decrease of thermal stability, while under oxygen flow the resistance of oxidation and thermal stability of sPB/organoclay nanocomposites were significantly improved relative to pristine sPB. The primary and secondary crystallization for pristine sPB and sPB/organoclay (2%) nanocomposites were analyzed and compared based on different approaches.

Structures and elastic properties of OsN2 investigated via first-principles density functional calculations

The structure, elastic, and electronic properties of OsN2 at various space groups: cubic Fm-3m, Pa-3, and orthorhombic Pnnm were studied by first-principles calculations based on density functional theory. Our calculation indicates that the structure in orthorhombic Pnnm phase is energetically more stable compared with cubic systems. It is metallic, mechanically stable and contains diatomic N-N units with the bond distance 1.418 A. These characters are consistent with experimental facts that OsN2 is orthorhombic and metallic. The calculated bulk modulus 394 GPa is also the highest among the considered space groups, slightly larger than previous value 358 GPa. The calculated elastic anisotropic factors and directional bulk modulus showed that OsN2 possess high elastic anisotropy.

Naphthyl and thionaphthyl end-capped oligothiophenes as organic semiconductors: Effect of chain length and end-capping groups

Two series of oligothiophenes (OThs), NaTn and TNTn (n = 2-6 represents the number of thiophene rings), end-capped with naphthyl and thionaphthyl units have been synthesized by means of Stille coupling. Their thermal properties, optical properties, single crystal structures, and organic field-effect transistor performance have been characterized. All oligomers display great thermal stability and crystallinity. ne crystallographic structures of NaT2, NaT3, TNT2, and TNT3 have been determined. The crystals of NaT2 and NaT3 are monoclinic with space group P2(1)/C, while those of TNT2 and TNT3 are triclinic and orthorhombic with space groups P-1(-) and P2(1)2(1)2(1), respectively. All oligomers adopt the well-known herringbone packing-mode in crystals with packing parameters dependent on the structure of the end-capping units and the number of thiophene rings. The shorter intermolecular distance in NaT3 compared to NaT2 indicates that the intermolecular interaction principally increases with increasing molecular length. X-ray diffraction and atomic force microscopy (AFM) characterization indicate that the NaTn oligomers can form films with better morphology and high molecular order than TNTn oligomers with the same number of thiophene rings. The NaTn oligomers exhibit mobilities that are much higher than those for TNTn oligomers (0.028-0.39 cm(2) V-1 s(-1) versus 0.010-0.055 cm(2) V-1 s(-1), respectively).

A new 1D metal-organic coordination polymer with blue fluorescent emission: [Cd-2(1,10 '-phen)(2)(betc)(H2O)](n)

A new coordination polymer [Cd-2(1,10'-phen)(2)(betc)(H2O)](n) (1) (betc = benzene-1,2,4,5-tetracarboxylate, 1,10'-phen = 1,10'-phenanthroline) was hydrothermally synthesized from CdCl2.2.5H(2)O, H(4)betc and 1,10'-phen at 160 degreesC. It was characterized by IR, XPS, TG and single-crystal X-ray diffraction. Compound 1 possesses infinite chair-like chains which construct 3D framework through pi-pi interactions and the hydrogen bond interactions. The fluorescent spectrum study shows that compound 1 exhibits blue fluorescent emission in the solid at room temperature.

Effects R3+ on the photoluminescent properties of Ca2R8(SiO4)(6)O-2 : A (R = Y, La, Gd; A= Eu3+, Tb3+) phosphor films prepared by the sol-gel process

Using CaCO3, metal oxides (all dissolved by nitric acid) and tetraethoxysilane Si(OC2H5)(4) (TEOS) as the main starting materials, Ca2R8(SiO4)(6)O-2:A (R = Y, La, Gd; A = EU3+, Tb3+) phosphor films have been dip-coated on quartz glass substrates through the sol-gel process. X-ray diffraction (XRD), atomic force microscope (AFM), scanning electron microscope (SEM) and photoluminescence (PL) spectra as well as lifetimes were used to characterize the resulting films. The results of XRD indicated that the 1000 degreesC annealed films are isomorphous and crystallize with the silicate oxyapatite structure. AFM and SEM studies revealed that the phosphor films consisted of homogeneous particles ranging from 30 to 90 nm, with an average thickness of 1.30 mum. The Eu3+ and Tb3+ show similar spectral properties independent of R 3, in the films due to their isomorphous crystal structures. However, both the emission intensity and lifetimes of Eu3+ and Tb3+ in Ca2R8(SiO4)(6)O-2 (R = Y, La, Gd) films decrease in the sequence of R = Gd > R = Y > R = La, which have been explained in accordance with the crystal structures.

Phase behavior of rare earth manganites

Among complex oxides containing rare earth and manganese BaLn(2)Mn(2)O(7)( Ln = rare earth) with the layered perovskite type and Ln(2)(Mn, M)O-7 with pyrochlore-related structure were studied since these compounds show many kinds of phases and unique phase transitions. In BaLn(2)Mn(2)O(7) there appear many phases, depending on the synthetic conditions for each rare earth. The tetragonal phase of so-called Ruddlesden-Popper type is the fundamental structure and many kinds of deformed modification of this structure are obtained. For BaEu2Mn2O7 at least five phases have been identified from the results of X-ray diffraction analysis with the space group P4(2)/mnm, Fmmm, Immm and A2/m in addition to the fundamental tetragonal I4/mmm phase. In the pyrochlore-related type compounds, Ln(2)Mn(2-x)M(x)O(7)(M = Ta, Nb, W etc), there also appear several phases With different crystal structures. With regard to every rare earth, Ln(2)MnTaO(7) phase is stable only for excess Ta and can be obtained under high oxygen partial pressure process. This group has trigonal structure with zirkelite type ( P3(1)21 space group).

Fractionated crystallization of dispersed PA6 phase of PP/PP-g-MAH/PA6 blends

Fractionated crystallization behavior of dispersed PA6 phase in PP/PA6 blends compatibilized with PP-g-MAH was investigated by scanning electron microscopy (SEM), differential scanning calorimeter (DSC), polarized light microscopy (PLM), and wide-angle X-ray diffraction (WAXD) in this work. The lack of usual active heterogeneities in the dispersed droplet was the key factor for the fractionated crystallization of PA6. The crystals formed with less efficient nuclei might contain more defects in the crystal structures than those crystallized with the usual active nuclei. The lower the crystallization temperature, the lesser the perfection of the crystals and the lower crystallinity would be. The fractionated crystallization of PP droplets encapsulated by PA6 domains was also observed. The effect of existing PP-g-MAH-g-PA6 copolymer located at the interface on the fractionated crystallization could not be detected in this work.